Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Correct r228114 and use the same implementation for tilde.h as for history.h

Use INCSLINKS so that "make installincludes" installs links during buildworld.

- Hide _rl_qsort_string_compare() that should be private to libreadline()
implementation.
- Add symlink /usr/include/edit/readline/tilde.h -> readline.h

All this makes it possible to build and link gdb with -ledit.

Add $FreeBSD$'s.

* Add the readline(3) API to libedit. The libedit versions of
{readline,history}.h are in /usr/include/edit so as to not conflict with
the GNU libreadline versions. To use the libedit readline(3) one should
add "-I/usr/include/edit" to their Makefile
(spelled "-I${DESTDIR}/${INCLUDEDIR}/edit" within the FreeBSD source tree).

* Enable its use in the BSD licensed utilities that support readline(3).

* To make it easier to sync libedit development with NetBSD, histedit.h
is moved into libedit's directory as history shows shown we keep merging
it into that location.

Obtained from: NetBSD
Sponsored by: Juniper Networks